Electron discharge device



Now 1, 1938. B. n. H. TELLEGEN ET AL 2,134,396

ELECTRON DI SCZIARGE EE'V'I Filed April 19, 1338 INVENTOR. BERNARDUS D. H. TELLEGEN- MARC ZIEGLER A TTORNEY.

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Bernardus Dominicus Hubertus Tellegen and Application April 19, In Germany 3 Claims.

This invention relates to electron discharge tubes to be used in a circuit arrangement for the amplification or frequency transformation of electrical oscillations, in which at least the first tube comprises two or more electrodes at a positive potential.

As is well known, biasing occurs in radio arrangements from the coupling elements and from the tubes and more particularly from those coupling elements and tubes wherein the incoming signal has only a small amplitude, for instance, in the high frequency part of a radio receiving arrangement.

The principal object of our invention is to provide an electron discharge device particularly suitable for amplification or frequency transformation in which tube noise and hiss is reduced.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a schematic diagram of an electron discharge device made according to our invention and Figure 21s a modification of the electron discharge device shown in Figure 1 and employing our invention.

Extensive experiments indicate, especially in connection with hissing caused in the tube, particularly when used at high frequencies, that by making use of an arrangement of an electron discharge device according to the present invention hissing can be substantially reduced.

In a circuit arrangement for the amplification or frequency transformation of electrical oscillations wherein at least the first tube comprises two or more electrodes having a positive potential, the distribution hiss factor of the currents 40 and voltages used in the apparatus is, according to the invention, made smaller than l/8.

The fact that a screen grid tube involves more hissing than a triode was found to be due to accidental variations in the ratio between the According to the invention the oscillations of the anode current in a screen grid tube are reduced to a minimum by rendering the screen grid current or the variations of the ratio between the screen grid current and the anode current to be as small as possible.

In an amplifying arrangement or in a frequency transformation arrangement, in which the incoming oscillations and the locally produced oscillations are supplied to the same grid of a mixing 1938, Serial No. 202,820 March 17, 1937 tube the invention permits the distribution hiss factor to be made smaller than 1/8. we have found, however, that in frequency transformation arrangements, wherein the incoming oscillations and the locally produced oscillations are supplied to different grids in a mixing tube, this limit must be given a higher value, that is a distribution hiss factor of l/2.

The invention will be more clearly understood by reference to the following calculation. The i value of the oscillations of the stream of electrons issuing entirely independently of each other from a hot cathode, is represented by the Well-known expression for the shot effect:

3:5 1 wherein the contribution from a definite frequency band to the average square variations of the emission;

average emission current; Cztwice the charge of the electron times the width of the frequency band in question.

This formula holds good for the current variations of a saturated diode, in which all of the electrons issuing from the cathode pass to the anode. In cases wherein a potential minimum occurs due to the space charge in the vicinity of the cathode, so that part of the electrons returns to the cathode, a certain regularity evolves in the stream of electrons leaving the space charge, so that the variations of this current are smaller than the pure accidental variations which are expressed by the equation:

ii=Ffi.C.I,, (2) wherein the hiss factor Fi is smaller than 1.

Generally the hiss factor is to be understood to mean the ratio between the average square variations of a stream of electrons which pass entirely independently of one another and which stream has a uniform value on an average.

The regularity of the stream of electrons leaving a space charge may in practice be such that the hiss factor Pi is smaller than 0.05. In electron tubes, wherein the anode current forms only part of the total cathode current, the anode current may relatively and absolutely carry more variations than the cathode current due to the fact that the division of the total number of electrons in anode electrons and remaining electrons is accidental to a certain extent which involves distribution variations.

Consequently the hiss factor of the anode current Ia in cases, wherein the anode current is smaller than the cathode current, must be higher than the hiss factor of the cathode current For a definite ratio between I, and

R an upper limit of can be calculated by considering the electron distribution as a pure calculation of probabilities.

A calculation of probabilities shows that if the total current were perfectly uniform,

the hiss factor of the anode current would be:

the accident factor or being 1 if the distribution answers to pure accident laws, and smaller than 1 if the distribution takes place in conformity to certain geometrical laws. However, the stream of electrons originating from the space charge is never perfectly uniform, so that However, this stream may be imagined to be split up in a fraction TE=FIY with complete accidental variation (hiss factor :1) and a fraction Ik =(1F: Tk which is perfectly uniform (hiss factor=0).

The part of going to the anode, which part amounts to 7., 2 Tf ra current correspond to the sum of the independent contributions of and Thus we have, in accordance with (2):

i= iZl+ all (4) Now, per definition:

so that F2: z+[ %]ca) (s) In an electron discharge tube having one or the two members of the right hand part of (6) should be small. In the first place the hiss factor of the cathode current, in the second place the factor which will be called the distribution hiss factor According to (6) it has a value and can be determined experimentally for any electron discharge tube.

These considerations apply for an arbitrary number of positive grids in the tube. However, it was taken for granted that the grids had a constant voltage. When (in a mixing tube) one of the grids has an alternating voltage, whose frequency is not low in comparison with the frequencies of the band transmitted on the anode side, the relations inferred no longer hold good. In contradistinction thereto it will be obvious that if for the whole cycle of adjustments traversing the tube, the hiss factors, considered statically (for which case the formulae apply) be as favorable as possible, the hiss factor of the tube during operation will also be as favorable as possible. Thus, the means for keeping the hiss factor of the anode current of a mixing tube as low as possible correspond to those referred to above.

The invention has for its purpose to make the distribution hiss factor as small as possible and more particularly smaller than A; for amplifying arrangements and frequency transformation arrangements, in which the received oscillations and the locally produced oscillations are supplied to the same grid of the first detector tube, and smaller than A for frequency transformation arrangements in which the received oscillation and the locally produced oscillations are supplied to different grids of a mixing tube. This can be ensured in various ways. Priwith each other or extend in one plane.

marily the ratio in a screen grid tube may be made as small as possible, i. e. the screen grid current may be reduced to a minimum. In an arrangement ac cording to the invention an electron discharge tube may be used for this purpose, the electrode system of which tube includes, among other electrodes, a screen grid and in which tube the active parts of the screen grid, seen in the direction from the cathode to the anode normally to the cathode surface, lie in the shadow of the active parts of one or more grids arranged between the cathode and the screen grid.

According to a particular form of construction of the present invention the high frequency part of a radio receiving arrangement comprises a tube having a control grid with variable pitch, and in which the screen grid arranged behind the control grid is Wound so as to be variable substantially in the same manner as the control grid.

For solving the problem put with the invention it is not necessary to use grids wound with a variable pitch, since it is also possible to use grids known arranged one behind the other and not wound with a variable pitch.

In frequency transformation arrangements in which the local oscillations and the received oscillations are supplied to two different grids in the mixing tube the active parts of all grids might be arranged in their respective shadows. However, this has the objection that the control grid remotest from the cathode has an insufiicient control effect on the stream of electrons which may involve serious difiiculties more particularly when this grid is used as an input control grid. For this reason it is well-nigh impossible in. such a mixing tube to arrange all grids one behind the other, so that the distribution hiss factor is always larger than in a high frequency amplifying arrangement or in a frequency transformation arrangement, in which the local and received oscillations are supplied to the same grid.

Another method of making the distribution hiss factor as small as possible is to make the accident factor a as small as possible. This is achieved when each of the current conveying electrodes receives its electrons from a different part of the space charge, which part is as independent as possible. They may be efiected by means of such a construction of the screen grid that the cathode can be imagined to consist of two or more parts, substantially all the electrons emitted by one part passing to the anode and substantially all of those emitted by another part passing to the screen grid. For this purpose an electric discharge tube may be used whose electrode system includes, inter alia, a screen grid and in which this screen grid consists of plateshaped parts.

Finally a combination of these two measures may be used.

In the drawing the envelope l of a tube encloses a cathode 2, a control grid 3, a screen grid 4 and an anode 5. As appears readily from the drawing the tube shown in Figure 1 is provided with a control grid and a screen grid both of which are wound with a variable pitch and whose active parts, seen in a direction from the cathode to the anode normally to the cathode register The screen grid 4 forming part of the tube shown in Figure 2 may consist of fiat ribbon wound as a helix or may be of plate-shaped parts if the electrodes are planar. The electrodes are preferably concentricate in which case grid 3 may be wound as a double helical grid, that is the grid includes a pair of spaced interspersed helical wires wound in the same side rods. This permits positioning of the outer concentric ribbon grid so that its solid portion registers with alternate spaces between the turns of the wires and the space between the turns of the ribbon grid registers with other alternate spaces between the turns of the wire grid. If the wire grid comprises a plurality of parallel rings, the ribbon grid may comprise a plurality of parallel rings registering with alternate spaces between the wire rings.

The circuit associated with the tube shown in Figure 2 comprises an input circuit 6 connected between the cathode 2' and the control grid 3', and an output circuit 1 connected to the anode the screen being biased by a proper connection to the source of voltage supply 8,

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

1. An electron discharge device having an envelope containing a cathode and an anode and at least two grids between the cathode and anode, the grid next to said cathode comprising spaced wires and the grid closer to the anode comprising spaced flat members of greater projected area than the Wire members of the grid next to the cathode, each of said flat members registering with a space between two adjacent wire members, and each of the spaces between the fiat members registering with a space between two adjacent wire members.

2. An electron discharge device having an envelope containing a cathode and anode, at least two grids between the cathode and anode, the grid closer to the cathode including a pair of spaced interspersed helical wires and the grid closer to the anode including a helical ribbon grid, the solid portions of the ribbon grid registering with the alternate spaces between the grid wires, and the space between the turns of the ribbon grid registering with the other alternate spaces between the grid wires.

3. An electron discharge device having an envelope containing a cathode and anode, at least two grids between the cathode and anode, the grid closer to the cathode comprising a wire grid of a number of turns and the grid closer to the anode comprising a ribbon grid of a number of turns, each turn of the ribbon grid registering with the alternate space between two adjacent grid wires and the spaces between the turns of the ribbon grid registering with the other alternate spaces between two adjacent grid wires.

BERNARDUS DOMINICUS HUBERTUS TELLEGEN. MARC ZIEGLER. 

